The most appropiate Webserver Permission on ubuntu 16.04

I set up a server with Ubuntu 16.04, LAMP stack and wordpress. I have my server configured and setup on a VPS, running Ubuntu 16.04. When I first installed wordpress I couldn’t install any plugins at first, so I had permission setup like this:

sudo chown -R sammy:www-data /var/www/html sudo find /var/www/html -type d -exec chmod g+s {} ; sudo chmod g+w /var/www/html/wp-content sudo chmod -R g+w /var/www/html/wp-content/themes sudo chmod -R g+w /var/www/html/wp-content/plugins sudo chown -R www-data /var/www/html

After I did all of this I was able to install plugins but

1. I have not been able to submit forms - error message: There was an error trying to send your message. Please try again later.

2. The website constantly lost connection with error message: error connnecting to database

What will be the most appropriate permission and privilege to give to the Webserver to perform any future task that is needed